1. Field of the Invention
The present invention relates to a control unit for an electronic musical instrument, and more particularly to a control unit for an electronic musical instrument which is suitable for controlling tone pitch, tone color, tone volume and the like of a musical tone.
2. Prior Art
Some conventional electronic musical instruments provide pitch-bend units (see Japanese Patent Publication No. 61-47433, i.e., U.S. Pat. No. 4,347,772) each of which can continuously and arbitrarily change the tone pitch of musical tone by a manual operation of a switch and the like. FIG. 1 is a perspective side view showing partial constitution of an operation portion of such pitch-bend unit. In FIG. 1, 1 designates a wheel to be operated by a player, and this wheel 1 is mounted to a rotation shaft 2a of rotary volume (or rotary controller) 2. The voltage obtained at an edge of sliding element of this rotary volume 2 is supplied to an analog-to-digital (A/D) converter 3 shown in FIG. 2, wherein this voltage is converted into a digital signal which is to be supplied to a central processing unit (CPU) 4. Based on the data value of such digital signal, the CPU 4 controls a tone pitch of musical tone signal to be generated from a tone source circuit 5. In addition, the rotation shaft 2a of rotary volume 2 is mounted with a return spring 6. By elastic force of this return spring 6, the rotation shaft 2a is returned to its center position. When the player revolves the wheel 1 in the forward or backward direction while depressing a key of an electronic musical instrument, the tone pitch of a musical tone to be generated is raised or lowered from the reference tone pitch of the depressed key in response to a revolution angle of this wheel 1. Thus, it is possible to obtain the musical effect which can be caused by operating a tremolo arm of an electric guitar, for example.
In the above-mentioned conventional unit, the revolution angle of wheel 1 must be enlarged in order to largely change the tone pitch of a musical tone. However, such operation is difficult for the player. In some cases, the tone pitch is to be vibrated as it is in a vibrato performance. However, it is extremely difficult to play such performance by revolving the wheel 1.
Further, due to the variation of the return spring 6 whose elastic force will be varied in the lapse of time, its central position must be varied so that the tone pitch of a musical tone will be sometimes returned and fixed at the tone pitch which is undesirably shifted from the reference tone pitch thereof. Furthermore, this rotary volume 2 requires the A/D converter 3, which will raise the cost of this unit.